Other important resources are fossil fuel that is coal and petroleum which are important resources of energy for us. These are non-renewable sources of energy. Coal and petroleum were formed hundreds of million years ago as a result of the action of heat and pressure on decaying, buried plants in the swampy areas of the earth. The disadvantages of fossil fuels are that they release carbon dioxide, oxides of nitrogen and oxides of sulphur on combustion. Carbon dioxide causes global warming. Thus we need to use these resources judiciously.
Some alternative sources of energy are wind, solar, thermal and hydroelectric energy. These are all viable options since they are more environment-friendly. Energy conservation can be done by recycling and reusing plastic bags, switching off lights, and also by using CFL bulbs. Fuel is most commonly used in internal combustion engines for transportation and recent in this field concentrates on ensuring complete combustion in these engines in order to increase efficiency and also reduce air pollution.